This invention generally relates to improvements in the formulation and production of marine antifouling compositions and more particularly, to organotin-based antifoulants for epoxy coatings.
In the past, salts and oxides of metals such as copper, zinc, arsenic and mercury have been used in marine antifouling coatings. However, some of these compounds cause corrosion of the metal substrate and degradation of the paint coatings, as well as having a limited service life. Organotin based antifoulants such as tributyltin oxide and tributyltin fluoride have been developed to overcome some of the abovementioned drawbacks with the prior antifoulants. Although the organotin antifoulants are compatible with conventional antifouling coating systems, most coating systems contain various water soluble pigments, fillers and binders so that the antifoulant leaches into the water at an uncontrolled rate. In attempting to control the leaching rate of the antifoulants, various polymeric compounds have been developed as exemplified, for example, by U.S. Pat. Nos. 3,016,369; 3,382,264; 3,930,971; 3,979,354; 4,064,338; 4,075,319; and 4,174,339.
However, the reaction process of combining organotin oxides and hydroxides with various polymeric materials to control leaching, as discussed in the abovementioned patents, is more complex and costly than conventional preparation processes for other antifoulants. For example, the reaction process disclosed in U.S. Pat. Nos. 3,979,354 and 4,075,319 generally involves the esterification of an organotin compound with the acid group of a vinyl polymer. This reaction process not only produces water as a reaction by-product but also involves the sequential use of various solvents which must be removed along with the water to obtain a solids solution. The solids are then dissolved in another solvent to prepare the final coating composition. The process of making organometallic antifoulants envisioned by the present invention eliminates reaction steps disclosed by the prior art by eliminating the production of water by-product and by utilization of polymeric materials and solvents therefore which reduces the number of solvation-distillation steps. It was also found that the particular polymeric materials used to react with the organotin antifoulant exhibits controlled leaching characteristics not contemplated by the prior art.
Epoxy coating formulations are generally exemplified by U.S. Pat. Nos. 3,301,795; 3,417,045; 3,532,538; 3,676,388; and 4,172,177. Although antifoulant materials have been incorporated into the epoxy matrix such as disclosed, for example, in U.S. Pat. No. 3,676,388, problems have been experienced in providing uniform dispersion of antifoulant throughout the coating and controlling the leaching rate of antifoulant therefrom. Also, controlled physical properties are difficult to obtain when incorporating organotin polymers in the epoxy matrix.